Chapter 4 The Components of the System Unit
The System Unit

Box-like case that contains computer’s electronic components

Sometimes called the chassis
What are common components inside the system unit?

Processor

Memory module

Expansion cards
o Sound card
o Modem card
o Video card
o Network interface card

Ports and Connectors
What is the motherboard?

Main circuit board in system unit

Contains chips, integrated circuits, and transistors

Also called system board
What chip packages are available?

single edge contact (SEC) cartridge

dual inline package (DIP)

flip chip-PGA (FC-PGA) package

pin grid array (PGA
Central Processing Unit
What is the central processing unit (CPU) ?

Interprets and carries out basic instructions that operate a computer

Also called the processor
What are the components of the CPU?

Control Unit

Arithmetic/Logic Unit (ALU)
What is the control unit?

Directs and coordinates operations in computer

Control unit repeats four basic operations:
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
Fetch - obtain program instruction or data item from memory

Decode - translate instruction into commands

Execute - carry out command

Store - write result to memory
What is a machine cycle?

Four operations of the CPU comprise a machine cycle

Also called instruction cycle

Instruction time (i-time) - time taken to fetch and decode

Execution time (e-time) - time taken to execute and store
An example of a machine cycle

Student enters math problem (100 x 52) into computer’s memory

Result in memory displays on monitor’s screen
How is the CPU’s speed measured?

According to how many millions of instructions per second (MIPS) it can process
What are two designs used for the CPU?

CISC (complex instruction set computing)
o Supports large number of instructions
o CPU executes complex instructions more quickly

RISC (reduced instruction set computing)
o Supports smaller number of instructions
o CPU executes simple instructions more quickly
What is the arithmetic/logic unit (ALU) ?

CPU component that performs execution part of the machine cycle
o Arithmetic (addition, subtraction, multiplication, and division)
o Comparison (greater than, equal to, or less than)
o Logical (AND, OR, NOT)
What is pipelining?

CPU begins executing second instruction before completing first instruction

Results in faster processing
What is a register?

Temporary storage area that holds data and instructions
o Stores location from where instruction was fetched
o Stores instruction while it is being decoded
o Stores data while ALU processes it
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o Stores results of calculation
What is the system clock?

Synchronizes all computer operations

Each tick is clock cycle

MHz megahertz (millions)

GHz gigahertz (billions)
What is a microprocessor?

Single processor chip found in personal computers
How do personal computer processors compare?

Intel - PC

AMD - PC

Motorola - Mac
What is a coprocessor?

Chip that assists processor in performing specific tasks

One type is a floating-point coprocessor, also known as a math or numeric coprocessor
What is parallel processing?

Using multiple processors simultaneously to execute program faster

Requires special software to divide problem and bring results together
Data Representation
How do computers represent data?

Most computers are digital

Recognize only two discrete states: on or off
What is the binary system?

Number system with two unique digits: 0 and 1
What is a byte?

Eight bits grouped together

256 characters
What are three popular coding systems to represent data?

ASCII - American Standard Code for Information Interchange

EBCDIC - Extended Binary Coded Decimal Interchange Code

Unicode - coding scheme capable of representing all world’s languages
How is a character sent from keyboard to computer?

Step 1: Press letter T

Step 2: Electronic signal for letter T sent to system unit
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
Step 3: Signal changed to its ASCII code (01010100) and stored in memory

Step 4: After processing, binary code for letter T is converted to image on output device
Memory
What is memory?

Temporary storage area for operating system, application programs, and data

Consists of one or more chips on motherboard

Each byte stored in unique address
How is memory measured?

By number of bytes available
o KB
o MB
o GB
o TB
What are two types of system unit memory?

volatile memory
o Loses its contents when computer's power
is turned off

nonvolatile memory
o Does NOT lose its contents when computer’s power is turned off
What is random access memory (RAM)?

Memory chips that can be read from and written to by processor

Most RAM is volatile

The more RAM a computer has, the faster it operates
What are two basic types of RAM chips?


Dynamic RAM (DRAM)
o
Most common type
o
Also called main memory
Static RAM (SRAM)
o
o
Used for special applications such as cache
Faster and more reliable than DRAM chips
How much RAM is needed?

Software package usually indicates RAM requirements
How much RAM is needed?

Depends on type of applications you intend to run on your computer
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What is cache

Helps speed computer processes by storing frequently used instructions and data

Also called memory cache, cache store, or RAM cache

L1 cache built in processor

L2 and L3 cache not built in processor

L2 advanced transfer cache most common
What is read-only memory (ROM)?

Memory chips that contain data, instructions, or information that is recorded permanently

Data can only be read; cannot be modified in ROM

ROM is nonvolatile — Contents not lost when computer is turned off
o BIOS (basic input/output system)
o Stored on ROM

Sequence of instructions computer follows to load operating system and other files when you turn
on the computer
Types of ROM

Firmware

ROM chips manufactured with permanently written data, instructions, or information

PROM (programmable read-only memory)
o Blank ROM on which you can place items permanently

EEPROM (electrically erasable programmable read-only memory)
o Type of PROM containing microcode programmer can erase
What is flash memory?

Nonvolatile memory that can be erased electronically and reprogrammed

Used with handheld computers and digital cameras, cellular phones, and automobile
What is CMOS?

Complementary metal-oxide semiconductor memory

Stores information about the computer
o type of disk drives
o keyboard
o monitor
o current time and date

Uses battery to retain information when computer is turned off
What is memory access time?

Speed at which processor can access data from memory directly
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
Measured in nanoseconds (ns), which is one billionth of a second

It takes 1/10 of a second to blink your eye; a computer can perform up to 10 million operations in
same amount of time
Expansion Slots and Expansion Cards
What is an expansion slot?

An opening, or socket, where circuit board is inserted into motherboard

Expansion card inserted in expansion slot
How are expansion cards used?
What is Plug and Play?

Computer automatically can configure cards and other devices as you install them
What is a PC card?

Credit card-sized device used to add capabilities to notebook computers

PCMCIA - Personal Computer Memory Card International Association

Uses include modem, additional memory, and storage
o Memory – Type I
o Modem – Type II
o Hard Drive – Type III
What is a flash memory card?

Adds memory to handheld computers, digital music players, cellular telephones,
and similar devices
Ports
What is a port?

Connects external devices to system unit
o keyboard port
o USB port
o serial port
o monitor port
o game port
o network port
o mouse port
o parallel port
o speaker port
o microphone port
What are different types of connectors?
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What is a serial port?

Transmits one bit of data at a time

Used to connect slow-speed devices, such as mouse, keyboard, mode
What is a parallel port?

Connects devices that can transfer more than one bit at a time, such as a printer
What is a universal serial bus port (USB) ?

Connector that supports newer peripherals and plug and play

Can connect 127 devices

Other popular ports include 1394, MIDI, SCSI, and IrDA
Buses
What is a bus?

Channel that allows devices inside computer to communicate with each other

On the motherboard

System bus connects processor and RAM

Bus width determines number of bits transmitted at one time

Word size determines number of bits processor can interpret
and execute at a given time
o Usually same as bus width
What is an expansion bus?

Allows processor to communicate with peripherals
o ISA – most common, slowest
o Local Bus – high-speed, connects higher speed devices
o AGP – designed by Intel to improve 3-D graphics
Bays
What is a bay?

Open area inside system unit used to install additional equipment
Power Supply
What is a power supply?

Converts alternating current (AC) to direct current (DC)

Some peripheral devices have AC adapter
Mobile Computers
What is a mobile computer?

Notebook, which weighs between 2.5 and 8 pounds, or handheld
What ports are on a notebook computer?
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
Keyboard/mouse port

IrDA port

Serial port

Parallel Port

Video port

USB port
How is data transferred from a handheld computer?

An IrDA port allows the handheld computer to communicate wirelessly with other computers or
devices

Handheld computers also can rest in a cradle, so you can transfer data to your desktop computer
Putting It All Together
What are suggested processor, clock speed, and RAM requirements based on the needs of various
types of users?

Pentium® 4 or Itanium™ or Athlon™ 1 GHz or higher

256 MB RAM
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